Congenital cardiovascular malformations are the most common birth defect and contribute to the morbidity and mortality of our cardiovascular patients. The long range goal and the clinical significance of this proposal are to decipher the networks that govern the progenitors during endothelial development and regeneration. Our laboratory discovered Etv2/Etsrp71/ER71 as a transcriptional target of Nkx2-5 and demonstrated that Etv2 regulates the differentiation of endocardial/endothelial lineages. Additional studies further defined that Etv2 mutant embryos were nonviable and had perturbed mesodermal (endothelial, hematopoietic and cardiac) lineage development. Based on our novel results, our overall hypothesis is that Etv2 is an essential factor for the master molecular program for the endothelial lineage during development and regeneration. In these proposed studies, we will utilize a number of novel genetic models that we have engineered and take an innovative approach to dissect the role of Etv2 as a regulator of endothelial progenitors. To examine our hypotheses, we will address the following specific aims: Specific Aim #1: To define the regulation of the Etv2 gene during embryogenesis; Specific Aim #2: To define the functional role of microRNAs for the specification and differentiation of the endothelial lineage and Specific Aim #3: To define the cell fate of the Etv2 expressing cells during development and regeneration. These aims will utilize our recently engineered genetic mouse models and ES cell lines to comprehensively define the role for Etv2 as an essential endothelial regulator and will serve as prelude for therapeutic initiatives to engineer and regenerate the vasculature. Given the tremendous morbidity and mortality of cardiovascular disease in our society, the potential impact of this proposal is significant.